In a typical head, an inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being located between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium. Since magnetic flux decays as it travels down the length of the narrow second pole tip, shortening the second pole tip will increase the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS.
FIG. 1 illustrates, schematically, a conventional recording medium such as used with conventional magnetic disc recording systems. This medium is utilized for recording magnetic impulses in or parallel to the plane of the medium itself. The recording medium, a recording disc in this instance, comprises basically a supporting substrate 100 of a suitable non-magnetic material such as glass, with an overlying coating 102 of a suitable and conventional magnetic layer.
FIG. 2 shows the operative relationship between a conventional recording/playback head 104, which may preferably be a thin film head, and a conventional recording medium, such as that of FIG. 1.
FIG. 3 illustrates schematically the orientation of magnetic impulses substantially perpendicular to the surface of the recording medium. For such perpendicular recording the medium includes an under layer 302 of a material having a high magnetic permeability. This under layer 302 is then provided with an overlying coating 304 of magnetic material preferably having a high coercivity relative to the under layer 302.
Two embodiments of storage systems with perpendicular heads 300 are illustrated in FIGS. 3 and 4 (not drawn to scale). The recording medium illustrated in FIG. 4 includes both the high permeability under layer 302 and the overlying coating 304 of magnetic material described with respect to FIG. 3 above. However, both of these layers 302 and 304 are shown applied to a suitable substrate 306.
By this structure the magnetic lines of flux extending between the poles of the recording head loop into and out of the outer surface of the recording medium coating with the high permeability under layer of the recording medium causing the lines of flux to pass through the coating in a direction generally perpendicular to the surface of the medium to record information in the magnetically hard coating of the medium in the form of magnetic impulses having their axes of magnetization substantially perpendicular to the surface of the medium. The flux is channeled by the soft underlying coating 302 back to the return layer (P1) of the head 300.
FIG. 5 illustrates a similar structure in which the substrate 306 carries the layers 302 and 304 on each of its two opposed sides, with suitable recording heads 300 positioned adjacent the outer surface of the magnetic coating 304 on each side of the medium.
As perpendicular heads become smaller to accommodate ever increasing data density, fabrication processes must be adapted to properly create the fragile structures that will ultimately form the head. Current fabrication methods are not capable of adequately and consistently forming pole tips to the scale and tolerances required for modern disk drives.
One proposed process uses a patterned photoresist mask 602 formed above a pole tip layer of magnetic material 604 and a layer of nonmagnetic material 606 such as Al2O3. The structure 600 is shown in FIG. 6. The structure 600 is milled to form the pole tip from the layer of magnetic material 604. The resulting structure 700 is shown in FIG. 7. While the process forms a pole tip 702 with the desired tapered cross-section, there are several disadvantages. First, this process does not scale easily below 0.25 μm, which is necessary for high data density drives. Second, the resist 602 does not have an acceptable mill resistance, i.e., too much of the mask 602 is consumed in the mill process. The result is that the pole tip is sometimes damaged by the milling. Third, removal of the resist 602 is necessary at the pole tip 702 without knocking over or destroying the pole tip 702. However, milling inherently produces redeposition 704, which tends to form on the sides of the resist 602, and may even encapsulate the resist. This redeposition makes removal of the resist 602 more difficult, as solvent has a harder time reaching the resist-pole tip interface. If any resist 602 remains coupled to the pole tip 702, attempted removal of the resist 602 tends to tip the pole tip 702 over. Further, some of the resist 602 may be entirely encapsulated by the redeposition. This is unacceptable, as having a layer of soft polymer (resist) at the ABS causes hard disk drive tribology issues, i.e., head-disk interface problems such as wear, water uptake, swelling, etc. Rather, it is desirable to have only hard materials at the ABS.
Another proposed process uses an alumina hard mask layer 802 above a pole tip layer 804. Instead of photoresist, a layer of NiFe (nonmagnetic) 806 is plated on top of the hard mask layer 802 and trimmed and notched to form the structure 800 shown in FIG. 8. Then, the structure 800 is milled to form the pole tip 902, as shown in FIG. 9. This process avoids having to remove photoresist, but the extended milling required to mill through the layer of NiFe 806 and alumina hard mask layer 802 create cavities adjacent to the pole tip 902. Thus, the desired tapered shape of the pole tip 902 is difficult to achieve. Further, if further processing is to be performed above the pole tip 902, the layer of NiFe 806 and possibly the alumina hard mask layer 802 may need to be removed to reduce the overall head size and provide a smooth surface upon which to add the additional layers. Removal of these layers without damaging the pole tip 902 is difficult.
What is needed is a method of fabricating pole tips of very small scale while overcoming the aforementioned disadvantages.